Television receiver



Feb. 6, 1940. KARQLUS 2,189,315

TELEVIS ION RECEIVER Filed May 1, 1937 2 Sheets-Sheet 1 INVENTOR /8 1/ 2 AUGUST KAROL us ATTORNEY Feb. 6, 1940. A. KAROLUS TELEVISION RECEIVER Filed May 1, 1957 2 Sheets-Sheet 2 INVENTOR AUGUST KAROLl/S BY kg WW ATTORNEY Patented Feb. 6, 1940 UNITED STATES TELEVISION RECEIVER August Karolus, Leipzig, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application May 1,1937, Serial No. 140,152 In Germany May 6, 1936 4 Claims.

In order to receive television images on a projection screen, whereby said images are transmitted on a channel, in other words for the reconstruction of television images in the receiver, attempts have been made to project the image ofthe fluorescent screen of a Braun tube. In fact, this suggestion permits of producing with comparatively satisfactory brightness, images whose size is below 1 mF, but serious difliculties are encountered when attempting projection of television receiving images on a screen surface of the size of about that of a movie screen, i. e., on a surface of about m. To this end it would be necessary-even when assuming that the fluorescent mass would be such as to supply the required luminous currentsto increase the voltage as well as the current amperage of the cathode ray to values that make their control entirely impossible. Furthermore, at such a high voltage the X-rays released by the cathode ray impingement in the fluorescent mass would cause a very great disturbance. In present day Braun tubes for projection piuposes the voltage values of about kv., and current values of about 3 ma. in use produce inconvenient effects. In fact a uniform brightening-up of the entire fluorescent screen is hereby produced, which can be explained only through the appearance of X- rays. Even at a voltage of 15 1a., and a cathode ,6 ray current of 3 ma. only a current of light is obtained on the screen surface that is 200 to 400 times smaller than the luminous current on an ordinary movie screen.

In order to overcome these difficulties, in accordance with the invention a multiplicity of cathode ray systems comprising fluorescent screens are so to say placed in parallel, so that each cathode ray system is permitted to bombard its fluorescent screen during a time that is longer than that available for transmitting the respective image element. In this case, the current in the individual cathode ray systems can be controlled by means of a cathode ray switch in which each contact element assigned to one cathode ray system is engaged by the switching cathode ray only for about the length of time in which the respective brightness value to be imparted to the image element is televised. The

Cir

switch sets each cathode ray system so that therein an electron bombardment of the fluorescent screen occurs even after the switching ray has again moved away from the contact element. Hence, the luminous currents coming from the individual fluorescent screens impinge on the screen surface at a very considerable time overlapping.

The invention therefore resides in the combination of a cathode ray switch and a multiplicity of parallel connected cathode ray systems co each having a fluorescent screen, each of which after the setting by the cathode ray switch, 1r radiates its fluorescent screen during a longer time than that in which the switching cathode ray remains on the appertaining contact ele- Fig. 6 shows an arrangement of cathode ray systems, and

Figs. '7, 8, 9 are particular constructions of the cathode ray tube.

In Fig. 1, I designates a glass bulb containing a cathode H, a control organ H such as for instance a Wehnelt cylinder, and an anode it, as well as a multiplicity of contacts I 4 through I! being illustrated, provided with separate leadins. The anode I3 is maintained at a positive potential relative to the cathode by means of a direct potential source i 8. The contacts M are connected to the grounded positive pole of the potential source I8 across a respective RC-element l9 and a common direct potential source 22, this connection line also containing a potential source 22 having its positive terminal joined to the RC-elements. Each of the contacts l4, etc., is also connected to the control organ of a cathode ray system comprising a fluorescent screen, shown in Fig. 1 schematically only, by'a triode 23 with a direct potential source 24 inserted in its cathode lead-in. Th term RC- element used herein means a resistance-capacity circuit or time constant circuit.

To explain the functioning of the arrangement according to Fig. 1, it isassumed that across the control electrode l2 designated by the term image there will be applied either the high or intermediate frequency potential modulated with the image content, or the voltage supplied by a detector circuit. The cathode ray of the switch thus varies its intensity in .accordance with the pattern of the image brilliancy and is caused to sweep over the contacts l4; l5, l6, e't c., arranged along a line, or along a circle,

said sweeping being obtained by means of a' saw-tooth shaped deviation field, or by means of a rotary field. This ray may remain on each of the contacts as long as the brightness of an image point is transmitted. Viewed in the direction of the electron passage, the ray current then passes from the cathode to the one of the contacts l4, l5, 16, etc., through one of the condensers of the RC-members I8, 20, 2 I, etc., across the potential source 22 and I8, and back to the current, multiplied by the duration of an image point BPD.

' g I Q=i .BPD

This charge furnishes at the condensers a voltage E determined by the quotient formed by the charge and the capacity C.

Since the ray current i varies, the voltages applied to the individual condensers dii fer likewise. During the time elapsing until the cathode ray returns upon the respective contact element, the condenser potentials dissipate themselves across the parallel connected resistors, thus prevailing for a considerably longer time although the value thereof decreases, than the time in which the cathode ray touches the appertaining contact element, i. e., during a time which is much longer than the duration of the imagepoint Since the voltage is built up at the individual condensers with the speed of succession of the individual image points, there is always a multiplicity of condensers eifective at the same time, i. e., the cathode ray systems comprising fluores cent screen are so-to-say connected in parallel,

since the operating periods thereof extending throughout the entire discharge period of the condensers, overlap each other.

Another mode of construction for the cathode ray switch is shown in Fig. 2, and differs from I that of Fig. 1 in that in addition a second anode 25 is provided, maintained relative to the anode I 3 at a positive potential by-the potential furnished by the direct voltage source 26, and serving for further acceleration of the cathode ray beam and also for its concentration. Otherwise, the functioning of the arrangement according to Fig. 2 is the same as that described on hand of Fig. 1.

Instead of having the condensers of the RC- members i9, 2!], 2 I, etc., charged by the ray current as explained in connection with the Figs. 1 and 2, it is possible in changing the poles of the direct potential. source 22 to utilize the secondary electrons appearing on the contact i l, I5, etc.,

A for charging the condensers.

To explain this mode of operation, the known phenomena of secondary emission will again be briefly reviewed in connection with Figs. 3 and s. In Fig. 3, the reference characters H to i3 and i8 designate the same means as in Fig. 1. An absorption plate M which is cap-able of secondary emission is connected by direct contact with the anode 13 across the direct voltage source U having the poles reversed as compared with the direct voltage source 22- shown in Fig. 1. Items i s, is designate three current meters placed in the cathode lead in, in the lead-in for the anode and in the lead-in for the absorption plate l4. At a certain ray amperage i there is observed-the current pattern designated by 111 in Fig. 4 in relation to the voltage U whose polarity indicated in Fig. 3 corresponds to the prnitive abscissa axis in Fig. 4, and for a higher amperage of the ray i the pattern designated by is is observed. As long as the voltage U- is negative, 1. e., as long as the latter while the current is equals zero.

absorption plate M has positive potential relative to the anode i3, and consequently, secondary electrons produced on this absorption plate cannot leave this plate. This condition corresponds with points of the curve situated to the left of the ordinate axis in Fig. 4. The current measured in the meter is hence, is equal to the current i However, if the voltage U has a considerable value (for instance higher than 15 volts) and if it has the polarity indicated in Fig. 3, there appears in the circuit M in addition to theray current (in circuit L) the recondary emission current of the plate M. This current has the direction indicated by arrows when viewed in the direction of the electron movement. The secondary electrons thus pass from the absorption plate M to the anode l3, being therefore a secondary emission anode, said electrons passing furthermore through the meter is, through the voltage source U, then meter is and back to the plate It. When the surface of the plate It is provided with a suitable material, this secondary emission current can be a multiple of the current i In the meter is in which the currents have opposite directions, there can thus only be observed the difierenceia between the secondary emission current is that can be fully measured in the instrument is, and the ray current ip. This condition has the corresponding curve points situated on the horizontal curve parts to the right of the ordinate axis in Fig, 4.

In order to operate on these curve branches, it is therefore only necessary to reverse the polarity of the voltage source in Figs. 1 and 2, so that condenser charges can thus be increased, and ,7

ence a more intensive control of the cathode ray systems equipped with fluorescent screen can be carried out. I

A still further mode of operation of the new arrangement can however also be explained by reference to Fig. 4. When operating with a nonvarying ray current i i. e., if thepctential of the control electrode !2 relative to the cathode l l is maintained invariable, the curve i1 or i2 in Fig. 4 is correct as already explained. If the voltage U in Fig. 3 is shown with the same polarity as in Fig. 3,.but its value chosen low as compared with the case previously explained, namely for instance equal to 61, ea. in Fig. l, the indicated Working points of the curve can be controlled in the and approximately straight region when connecting for instance, the image voltage varying with thebrightness of the image point, between the. voltage source 22 (whose negative pole must now be turned towards the RC-memhers) and the RC-members. Thus, also in this way a charge which varies in accordance with the respective brightness of the image point, can be supplied to each of the condensers in the RC- members. The steep curve branches in Fig. 4

Hence, the charge which the l correspond to an operating state in which the secondary emission current will be influenced in the same manner by the space charge of the secondary emission (in front of the plate [4) as is the case in an ordinary amplifier tube as re garcls the electron current in the so-called Langmuir space charge region.

Hence three different operating possibilities are available:

1. The condensers are charged only by the primary current. The potentials of the contacts l4, etc., are positive relative to the anode l3. The secondary electrons cannot leave the contacts (horizontal left hand curve branch in Fi 4) 2. The condensers are charged by the saturation current of the secondary emission. The potentials of the contacts l4, etc., have a negative value relative to the anode l3 that is higher than about 15 volts, said anode being now at the same time the anode for the secondary emission path I4'-i3. The secondary emission factor of the contacts I4, etc., must be greater than 2, if the condenser charges hereby obtained are to be higher than in case I (horizontal right hand curve branch in Fig. 4) I I 3. The contacts l4 are rendered but slightly negative relative to the secondary emission anode, and the space charge current of the secondary emission is used for charging the condensers (steep curve branch in Fig. 4).

Principally, the arrangements of the type described can be obtained by assigning to each image element of the entire television image, a cathode ray system comprising fluorescent screen. The time constant of the RC-members is then so dimensioned that each condenser will practically be discharged during the time for the entire image. The entire screen surface will then be reproduced on a projection screen.

An especially simple arrangement will be obtained when using a number of cathode ray systems corresponding to the image elements of the one image coordinate, and a photo-optical arrangement for instance a mirror wheel for the image reconstruction in the other image coordinate, and at the same time for the reproduction on the projection screen. In this way, the number of required switch contacts will be decreased, and on the other hand, it is possible conveniently to accommodate all cathode ray systems within one vacuum vessel, to provide respectively a common potential for their cathodes, or control grids, as well as their anodes, so that the number of the lead-in wires to be insulated from each other will be greatly reduced.

A form of construction for such common vacuum vessel is shown in Fig. 5 of the draw-. ings. Herein, 21 represents a tank-shaped glass vessel with U-shape cross-section on which is glued a. possibly plane parallel glass plate 28 by means of a glass enamel having a high melting point. The vacuum vessel contains a copper pipe 29 passed by cooling water, and which carries the fluorescent mass 30. The common anode of all cathode ray systems is designated by 3|, 2. control grid of one system is 32, and a common band-shaped cathode for all systems is designated by 33. The control grids of the individual systems may be advantageously equipped with springs 34 resting against the through-leads 35. The latter suitably consist of a colloidal gold deposit extending from the inside of the vessel up to its outside, and which can be fused into the said glass enamel binder. The copper tube 29 may have furthermore, a positive potential applied relative to the anode 3!, so that after the passing of the cathode'rays through the anode 3| a further acceleration takes place. Eventually, the copper tube 29 may also be utilized as a single anode.

Instead of bringing out the control grids 30 separately as shown in Fig. 5, also an indirectly heated cathode may be used, and the carriers of the active cathode material may be brought out separately. In this latter case, all control grids have a common fixed potential applied. The current is then controlled in each cathode ray system in that the individual cathode carriers receive a higher or lower potential relative to the common control grid.

Fig. 6 shows the manner in which the cathode ray systems are symmetrically arranged Within the common'vacuum vessel. The half of these systems has the axis 36, the other half, the axis 31.

Fig. 7 shows a further mode of construction for the common vacuum vessel, inwhich the fluorescent screens are provided on a closing-up wall of the vacuum vessel produced of metal and provided with cooling ribs. Instead thereof also a water-cooled closing-up wall composed of glass or of metal according to Figs. 8 and 9 can be used.

The cathode ray switch may also be eventually accommodated together with the cathode ray systems in the same vacuum vessel, as a result of which the total number of necessary insulated lead-in wires can still further be reduced very considerably.

What I claim is:

1. A television receiving apparatus for projection purposes comprising a cathode ray tube having a plurality of target members each representing an elemental area of the image to be reconstructed, means for modulating the cathode ray beam of said tube in accordance with received picture signals, means for directing said beam sequentially on said target members, means for storing a charge in accordance with the value of the beam striking a target member, a plurality of means for reconstructing elemental sections of the optical image, each of said reconstructing means being connected electrically to one of said target members, and means interposed between said image reconstructing means and said target member for maintaining the optical reconstruction of any section of'the picture for a time interval proportional to the charge stored by the target member representing that section of the picture.

2. An arrangement in accordance with claim 1 wherein each of said target members has a cathode ray associated therewith, and .all of said cathode ray and target member systems are enclosed within a common envelope.

3. An arrangement in accordance with claim 1 wherein the reconstructing device or the elemental sections of the picture is a cathoderay tube having a fluorescent screen, said screen being artificially cooled.

4. An arrangement in accordance with claim 1 wherein a device for reproducing each elemental area of the picture to be reconstructed is a cathode ray tube having a fluorescent screen, said screen being water cooled.

AUGUST KAROLUS. 

